Welding material for super low temperature steels

ABSTRACT

This invention provides a welding material for super low temperature steels which comprises not more than 0.2% carbon, 5 - 12% manganese, not more than 30% chromium, 4 - 8% niobium, 22% iron and not more than 1.5% silicon, the balance being substantially nickel, and which can give excellent strength and impact value to the weld zone. In one embodiment, the welding material is an integral body composed of a metal-forming material and a flux of lime or lime-titania in which the metal forming components are within the above range.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application of applicationSer. No. 242,202 filed Apr. 7, 1972, now U.S. Pat. No. 3,853,611.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a nickel-base alloy welding material for usein welding of steels which are intended to be subjected to super lowtemperature.

2. Description of Prior Art

Nine percent nickel steels are frequently used as lining materials forvessels for transporting super low temperature liquids, such asliquefied nitrogen, liquefied oxygen and liquefied natural gas. They arealso used in the construction of equipment used for processing orstoring super low temperature liquids. According to ASTM standards, 9%nickel steels are classified into A 353-65T (NNT steel) and A 553-65T(QT steel), and their properties are standardized. According to thisstandard, each of these types must have a tensile strength of 70.3 -84.4 Kg/mm², and the yield point (0.2% proof stress) for the NNT steelmust be above 52.7 Kg/mm², and for the QT steel must be above 59.8Kg/mm². The low temperature toughness at -196°C. must exceed 3.5 Kg-m.

Nickel steels of 5.5% have also become commercially available, but sofar there has been no standardization of such material. The strength andlow temperature toughness of such materials, however, are almost equalto those of 9% nickel steels.

It has been considered to use so-called eutectoid materials for 9%nickel steel and nickel-base alloys as the welding materials for theabove mentioned low temperature steels.

The eutectoid welding materials are of the same composition as that ofthe base metal and are characterized by a tensile strength and a yieldpoint equal to those of 9% nickel steels. However, since the lowtemperature toughness at -196°C. in the as-welded state, of theseeutectoid materials, is inferior to that of the base metal, they havenot been widely used.

Although nickel-base alloy welding materials are insufficient from thepoint of view of tensile strength (60-65 Kg/mm²) and yield point (0.2%proof strength) and 36 - 40 Kg/mm², respectively, for the depositedmetal, each of which is lower than the corresponding property of thebase metal, its low temperature toughness in the as-welded state isstable and excellent, and it has been primarily used for low temperatureapplications.

Welding materials of this type are classified as AWS A5.11 ENi-Cr-Fe 1to 3 and include so-called inconel alloys of 75Ni-15Cr series and alloysof 50Ni-15Cr and 35Ni-15Cr series, etc.

Since in such welding material a higher nickel content results in a highstrength and a more stable impact resistance, the inconel alloysfrequently find the greatest range of use.

ASTM standard 1308-5 specifies the properties required of the weld zoneso far as when stress relief annealing is not conducted in themanufacture of pressure vessels by welding of super low temperaturesteels, and this standard is usually adopted in this field. Thisstandard provides the requirements of joint tensile strength. Eventhough inconel alloys provide lower strengths of the whole depositedmetal than 9% nickel steels, they can nevertheless fully meet therequirements specified by ASTM 1308-5. In other words, any material thatcan provide a whole deposited metal strength of about 60 to 65 Kg/mm²can meet the standards of ASTM 1308-5, which means that this standardhas been determined by recognition of the fact that the strength of theweld zone may be lower than that of the base metal. In designingpressure vessels according to this standard, the lower strength weldzone must be considered, which results in a greater thickness ofconstruction than would be required if the weld zone were of equalstrength.

The Witherell reference U.S. Pat. No. 3,026,137 discloses the use of anickel chromium alloy which contains, in percent by weight, from about10% to about 30% chromium, up to about 8% iron, from about 2% to about3.5% titanium, up to 7% manganese, up to about 2% columbium, up to about0.5% silicon, up to about 0.1% carbon, and the balance essentiallynickel, with the nickel content being at least about 65%.

SUMMARY OF THE INVENTION

Accordingly, a primary object of this invention is to provide anickel-base alloy welding material which is free of the above-mentioneddefects of conventional welding materials and which can give excellentstrength and impact value characteristics to the weld zone in welding ofsuper low temperature steels.

Another object of this invention is to impart good workability to ahigh-manganese nickel-base alloy type welding rod.

These and other objects as will hereinafter become more readilyapparent, have been attained by the present invention which provides awelding material for super low temperature steels comprising not morethan 0.2% carbon, 5 - 12% manganese, not more than 30% chromium, 4 - 8%niobium, not more than 22% iron and not more than 1.5% silicon, thebalance being substantially nickel.

In another aspect, this invention provides a welding material for superlow temperature steels, which is formed by integrally combining ametal-forming material having the above composition with a flux of thelime or lime-titania type.

In still another aspect, this invention provides a welding material forsuper low temperature steels, which is formed by integrally combining ametal-forming material with a flux of the lime or lime-titania type inwhich the metal forming components are within the above range.

DETAILED DESCRIPTION OF THE INVENTION

The welding material of this invention can be used with any knownwelding method, such as manual welding, TIG welding or submerged arcwelding. By the term "welding material formed by integrally combining ametal-forming material with a flux" used in the instant specification ismeant a coated electrode for arc welding, composed of a core wirecovered with a flux; a composite wire composed of a metal casing packedwith alloy powder optionally together with a flux; or the like.

The nickel-base welding material of this invention has a compositioncomprising, on the weight basis, not more than 0.2% carbon, not morethan 12% manganese, not more than 30% chromium, not more than 8% niobiumand not more than 22% iron, the balance being substantially nickel, andit can be prepared by any conventional method. In addition to the aboveelements, the welding material of this invention generally comprisessilicon as a deoxidizing element and phosphorus and sulfur asimpurities. However, since these elements can adversely affect the crackresistance of the deposited metal, better results are obtained byreducing the silicon content to below 1.5% and the contents ofphosphorus and sulfur to below 0.1%.

The composition of the deposited metal formed by using the above corewire, can be calculated based on an assumption that the ratios ofcarbon, manganese, chromium, niobium, iron and silicon transferred fromthe core wire into the deposited metal, are 100%, 90%, 90%, 90%, 90%,and 60%, respectively.

A preferable coating material is one that can improve the ratios ofalloy-constituting elements transferred into the deposited metal and canreduce the generation of hydrogen. This object can be attained by theuse of flux having the composition of ordinary lime or lime-titania, inwhich a deoxidizing agent is present in an amount of up to 60%, and inwhich an alloy is incorporated in the form of a metal powder.

If the chemical composition of the nickel-base core wire is such thatthe above-described deposited metal composition specified would notordinarily have been obtained, it is nevertheless possible to obtainthese ratios by adding to the flux, as alloy-constituting elements, notmore than 1.6% carbon, not more than 55% manganese, not more than 60%chromium, not more than 24% niobium and not more than 10% silicon, withthe proviso that the total amount of these metals does not exceed 60%.

The above upper limits of each of the alloy-constituting elementsincorporated in the flux have been determined on the basis that thetotal deposited metal will have the above-mentioned composition in anintegral body composed of a nickel-base core wire having a relativelythin coating, i.e., a welding rod composed of a core wire and 25% byweight, based on the total welding rod, of the coating, and further onthe assumption that the ratios of carbon, manganese, chromium, niobium,silicon and iron transferred from the flux to the deposited metal are50%, 80%, 80%, 60% 60%, and 90%, respectively.

The effects attained by each of alloy-constituting elements will now bedescribed.

Nickel occupies the greater portion of the composition and is necessaryto attain low temperature toughness in the as-welded state. It isindispensable that the amount of nickel should be at least 45%. If thenickel content is lower than 45%, good low temperature toughness cannotbe obtained.

Chromium forms a solid solution with nickel to strengthen the matrix,and improves the tensile strength to a slight degree. It also acts toimprove the low temperature toughness. Thus, chromium is added in anamount of not more than 30%. If it exceeds this amount, the lowtemperature toughness will be greatly reduced by the addition of otherelements which are effective for increasing the tensile strength.

If the composition contains less than 5% of manganese, and thedifference is made up by increased quantities of niobium, the niobiumwill increase the tensile strength, but there will also be a tendencyfor the low temperature toughness to be abruptly decreased.

However, it has now been found that in compositions containing manganesein an amount of at least 5%, any increase in the niobium content willresult in improving the tensile strength with only a very littledecrease in low temperature toughness.

Manganese alone however, will not improve the mechanical properties ofthe alloy although it does exhibit a valuable effect in retarding thedegradation of the low temperature toughness. Such effect cannot beattained if the manganese content is less than 5%. However, the use ofgreater than 12% manganese will not enhance the above effectparticularly, but will result in poor workability in welding. Thus,manganese should be used in amounts from 5% - 12%.

Niobium, in combination with manganese, can conspicuously improve thetensile strength and it exhibits a valuable effect in increasing thecrack resistance of the deposited metal. For this reason, it may beincorporated in an amount of at least 4%. Less than 4% will beinsufficiently effective for enhancing tensile strength and cracksensitivity. If the niobium content is greater than 8%, the tensilestrength will become too high and the low temperature toughness will begreatly reduced.

Carbon and/or iron may be optionally added for specialty purposes.

Incorporation of a small amount of carbon will effectively improve thetensile strength but the low temperature toughness will be degraded to alarge extent and crack sensitivity will be increased. Therefore, thecarbon content should be not more than 0.2%.

Iron will increase slightly the tensile strength, but will tend toreduce low temperature toughness. However, since the degree of thisadverse effect is not significant, it may be used in amounts of not morethan 22%.

As described above, the objects of this invention can be attained by theuse of a flux of lime or lime-titania. If the manganese content isincreased in the nickel-base alloy composition, as in this invention,the deposited metal will become less "compatible" with the base metaland a slag will tend to be "burnt" which will be included into thedeposited metal with the result that workability in the weldingoperation will be reduced.

This defect can be overcome however by this invention, and goodworkability can be imparted to a high-manganese nickel-base alloywelding rod.

The flux according to this invention comprises, on the weight basis,10 - 50% calcium carbonate, 16 - 50% fluorspar, 2 - 20% magnesia clinkerand up to 10% rutile. An especially preferable flux is one containingmagnesia clinker and having a ratio of fluorspar to calcium carbonatewithin the range of from 1 to 1.5.

Not more than 60% of ingredients of such flux may be substituted by adeoxidizing agent, an alloy-constituting element or the like.

Each of the ingredients of the flux will now be described.

Calcium carbonate not only increases the basicity of slag but alsoshields the molten pool from air by generating CO₂ during welding. Italso forms CaO during welding which becomes incorporated into the slagto make it easily crumbling. It may be used, therefore, in amounts of10 - 50%. If the calcium carbonate content is below 10%, the molten poolwill not be shielded resulting in the formation of such defects asblowholes. If the calcium carbonate content exceeds 50%, the amount ofCO₂ gas generated during welding will be excessive and the arc will beunstable. Accordingly, a calcium carbonate content exceeding 50% is notpreferred.

The presence of CaO during welding, however, does tend to degrade thecompatibility of the weld metal. Therefore, it is necessary to blend thecalcium carbonate with fluorspar. It has now been found that the mostdesirable results are obtained when the ratio of fluorspar to calciumcarbonate is within the range of from 1 to 1.5.

Instead of calcium carbonate, of course, any alkaline earth metalcarbonate may be used with equally good results.

Fluorspar improves the compatibility of the weld metal and the peelingproperty of the slag. When used, it should be incorporated in an amountof 16 - 60%. The intended effects cannot be attained if the fluorsparcontent is below 16%. A fluorspar content exceeding 60% will result inan unstable arc. Instead of fluorspar, of course, other fluorides mayequally be used such as sodium fluoride, potassium fluoride, potassiumsilicofluoride, sodium silicofluoride, aluminum fluoride or any otherfluoride.

Magnesia clinker will act to stabilize the arc and will form a fireresistant coating covering. Thus, it may be used in amounts of 2 - 20%.If the magnesia clinker content is below 2%, such effects cannot beattained, and the peeling property of slag will be reduced.

The flux having the above composition can provide a welding rod of goodworkability, although the slag-peeling properties and the arc stabilitywill be further improved by the addition of not more than 10% rutile.When rutile is incorporated in an amount exceeding 10%, however, theviscosity of slag will be increased and the bead appearance will becomeuneven.

In order to provide the required composition of alloy elements to thedeposited metal, it is possible to substitute up to 60% of theingredients of the flux of this invention with a metal powder. If theamount of the metal powder exceeds 60%, however, the workability duringwelding will be adversely affected and the objects cannot be obtained.

Another embodiment of the process of preparing a welding material ofthis invention will now be described briefly by reference to a weldingrod.

The components of the lime or lime-titania coating material and theabove alloy components are blended together with water glass (an aqueoussolution of a mixture of sodium silicate and potassium silicate; 10 -20% based on the total weight of the welding rod. The assembly is driedat 200° - 250°C. Thus, the process is not particularly different fromthe conventional process of preparing welding rods.

Having generally described the invention, a more complete understandingcan be attained by reference to certain specific Examples, which areincluded herein for purposes of illustration only and are not intendedto be limiting unless otherwise specified.

EXAMPLE Welding material composition (1):

a. Chemical composition of core wire (%)

    C    Mn     Si     P     S     Cr    Nb  Fe   Ni                              ______________________________________                                        0.05 10.2   0.42   0.005 0.006 18.5  6.0 11.5 balance                         ______________________________________                                    

b. Blending ratios of ingredients of coating material calcium carbonate= 40%, fluorspar = 53%, rutile = 5%, ferrosilicon = 2% (silicon content= 50%)

c. Binder -- Aqueous solution of mixture of sodium silicate andpotassium silicate (SG 1.40)

d. Covering ratio of coating material -- 25% based on the total weightof the welding rod

Welding material composition (2):

a. Chemical composition of core wire (%)

    C    Mn    Si      P     S      Cr    Nb   Fe  Ni                             ______________________________________                                        0.06 1.2   0.55    0.04  0.006  14.0  1.5  7.3 balance                        ______________________________________                                    

b. Blending ratios of ingredients of coating material calcium carbonate= 28%, fluorspar = 31%, rutile = 2%, magnesia clinker = 4%, metallicmanganese = 15%, ferroniobium = 20% (niobium content = 70%)

c. Binder -- Aqueous solution of mixture of sodium silicate andpotassium silicate (SG 1.40)

d. Covering ratio of coating material -- 40% based on the total weightof the welding rod

Welding material composition (3):

a. Filler rod composition (%)

    C    Mn    Si     P     S     Cr    Nb   Fe   Ni                              ______________________________________                                        0.10 7.0   0.7    0.05  0.04  14.0  6.0  10   balance                         ______________________________________                                    

The above three welding materials (welding materials of compositions (1)and (2) are for arc welding using a coated electrode, and weldingmaterial of filler rod composition (3) is for MIG welding), and acommercially available nickel-base alloy welding rod having acomposition corresponding to that of ENi-Cr-Fe 3, were subjected totensile test, impact test and chemical analysis with respect to theas-welded deposited metal. Further, the tensile test and impact testwere conducted on the weld metal in the weld zone of 9% nickel steel.

Test Results

1. Chemical composition of the whole deposited metal:

A sample was collected according to AWS A511, and the chemical analysiswas conducted to obtain the following results:

     Welding rod (1) of this invention                                            C     Mn     Si      P     S      Cr   Nb    Fe                               0.05  9.17   0.40    0.004 0.006  16.8 5.40  10.94                             Welding rod (2) of this invention                                            C     Mn     Si      P     S      Cr   Nb    Fe                               0.06  5.88   0.33    0.004 0.005  12.6 4.71   8.66                             Welding rod (3) of this invention                                            C     Mn     Si      P     S      Cr   Nb    Fe                               0.09  6.80   0.65    0.004 0.006  13.5 5.8    9.7                              Commercially available Ni-base alloy welding rod                             C     Mn     Si      P     S      Cr   Nb    Fe                               0.03  6.82   0.52    0.005 0.004  13.5 1.72   9.20                        

2. Mechanical properties of the deposited metal:

The welding was conducted according to JIS Z 3221, and tensile testspecimens of JIS A No. 1 and impact test specimens of JIS No. 4 weretaken.

The tensile test was conducted at room temperature and the impact testwas effected at -196°C.

As is apparent from the test results shown in Table 1, in welding rodsof this invention, the deposited metal exhibited a tensile strength andductility comparable to those of 9% nickel steel base, together with asufficient low temperature toughness.

                  Table 1                                                         ______________________________________                                                   Tensile           Impact Value                                                Strength                                                                              Elongation                                                                              at-196°C.                                            (Kg/mm.sup.2)                                                                         (%)       (Kg-m)                                           ______________________________________                                        Welding rod (1) of                                                            this invention                                                                             79.1      41        6.1                                          Welding rod (2) of                                                            this invention                                                                             80.3      38        5.7                                          Welding rod (3) of                                                            this invention                                                                             79.6      38        6.5                                          Commercially avail-                                                           able Ni-base alloy                                                            welding rod  63.1      43        8.0                                          9% Ni steel    70.3 -                                                         standard     84.4      22        3.5                                          ______________________________________                                    

3. Mechanical properties of the weld metal in the weld zone of 9% Nisteel:

9% Ni steel specified in ASTM A 553-65T (QT steel) was subjected to thegroove welding, and mechanical properties of the weld metal diluted withthe base metal were examined. Two sheets of a dimension of 20 mm(thickness) × 250 mm (length) × 200 mm (width) were welded in a buttjoint to form a test specimen.

The groove conditions were as follows: a groove angle of 60°,a root faceof 0.5 mm, and a root gap of 1 mm. The surface side was metal-welded,and then the back chipping was effected, followed by one layer weldingon the back.

Tensile test specimens (D : φ G.L 50 mm) were taken in a directionparallel to the welding direction. Impact test specimens were takenaccording to JIS Z3111 (specimen No. 4).

The tensile test was conducted at room temperature, and the impact testwas effected at -196°C.

As is apparent from the test results shown in Table 2, in welding rodsof this invention, the weld metal exhibited a tensile strengthcomparable to that of the base metal and a sufficient low temperaturetoughness.

                  TABLE 2                                                         ______________________________________                                                   Tensile           Impact Value                                                Strength                                                                              Elongation                                                                              at -196°C.                                           (Kg/mm.sup.2)                                                                         (%)       (Kg-m)                                           ______________________________________                                        Welding rod (1) of                                                            this invention                                                                             77.6      42        6.3                                          Welding rod (2) of                                                            this invention                                                                             78.5      39        5.9                                          Welding rod (3) of                                                            this invention                                                                             76.3      38        6.0                                          Commercially                                                                  available Ni-base                                                             alloy welding rod                                                                          61.3      43        9.5                                          9% Ni steel  70.3 -                                                           standard      84.4     22        3.5                                          ______________________________________                                    

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit or scope of theinvention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A welding material which is suitable for lowtemperature steels, which comprises:a combination of metal-formingmaterial and a lime-titania flux, wherein said metal-forming materialand flux are combined in such a fashion that the integrity of the fluxand the metal-forming material as distinct entities is maintained insaid combination, said metal-forming material consisting of no more than0.2% carbon, 5 - 12% manganese, no more than 30% chromium, 4 - 8%niobium, no more than 22% iron, no more than 1.5% silicon, and thebalance being essentially nickel, and said flux consisting essentiallyof a mixture of 10 - 50% calcium carbonate, 16 - 50% fluorspar, 2 - 20%magnesia clinker and no more than 10% rutile and alloy-constitutingelements of no more than 1.6% carbon, no more than 55% manganese, nomore than 60% chromium, no more than 24% niobium, and no more than 10%silicon with the proviso that the total amount of the alloy constitutingelements in said flux does not exceed 60%, wherein all the elementscontained in the metal-forming material and flux are adjusted such thatthe composition, calculated on the basis of the metal-forming material,consists essentially of no more than 0.2% carbon, 5 - 12% manganese, nomore than 30% chromium, 4 - 8% niobium, no more than 22% iron and nomore than 1.5% silicon, the balance being essentially nickel.
 2. Awelding material which is suitable for low temperature steels, whichcomprises:a mixture of metal forming material and a lime-titania flux ina metal casing, said metal-forming material consisting of no more than0.2% carbon, 5- 12% manganese, no more than 30% chromium, 4 - 8%niobium, no more than 22% iron, no more than 1.5% silicon, and thebalance being essentially nickel, and said flux consisting essentiallyof a mixture of 10 - 50% calcium carbonate, 16 - 50% fluorspar, 2 - 20%magnesia clinker and no nore than 10% rutile and alloy-constitutingelements of no more than 1.6% carbon, no more than 55% manganese, nomore than 60% chromium, no more than 24% niobium, and no more than 10%silicon with the proviso that the total amount of the alloy-constitutingelements in said flux does not exceed 60%, wherein all the elementscontained in the metal-forming material and flux are adjusted such thatthe composition, calculated on the basis of the metal-forming material,consists essentially of no more than 0.2% carbon, 5 - 12% manganese, nomore than 30% chromium, 4 - 8% niobium, no more than 22% iron and nomore than 1.5% silicon, the balance being essentially nickel.